Accelerated atherosclerosis and premature aging of the cardiovascular system in patients with diabetes mellitus and metabolic syndrome have acquired epidemic proportions. Our previous studies of endothelial cells subjected to a microenvironment emulating the diabetic milieu revealed accelerated development of cell senescence. Based on the observations that the expression of nitrotyrosine-modified proteins was enhanced in the prematurely senescent cells and peroxynitrite treatment of intact cells led to premature senescence, we treated endothelial cells with a bona fide peroxynitrite scavenger/antioxidant ebselen. Such a treatment was associated with the prevention and reversal of premature senescence. These findings prompted us to investigate the molecular mechanism(s) of premature cell senescence, effects of ebselen on premature endothelial cell senescence in a model of metabolic syndrome - Zucker diabetic rats, and examine the development of vasculopathy in these animals. We hypothesize that oxidative stress/peroxynitrite-induced lysosomal dysfunction initiates endothelial cell senescence and accumulation of gangliosides, a molecular switch from senescence to apoptosis- events underpinning the progression of vasculopathy. In vitro and in vivo studies employing image analysis and fluorescence intravital microscopy, biochemical techniques to detect leakage of lysosomal and mitochondria! proteins as well as accumulation of gangliosides, and quntitative analysis of the markers of cell cycle are designed to investigate molecular and cellular mechanisms of premature senescence and apoptosis. In vivo studies of the Zucker diabetic fat rat treated with ebselen will be conducted to examine the possibility of preventing and reversing macro- and micro-vasculopathy (nephropathy) in this syndrome. The investigations may shed light on mechanisms of premature senescence of endothelial cells, role of peroxynitrite in initiating it, and potential therapeutic efficacy of peroxynitrite scavenging in amelioration of vasculopathy.